ath6kl: issue wmi disconnect after notifying cfg80211

ath6kl would issue a wmi disconnect command in response to a remote
disconnect and return early without notifying cfg80211, only sending a
cfg80211_disconnected (with reason code always 3) in response to the
second disconnect firmware event.

Pass the right reason code to cfg80211 on the first disconnect instead.

This fixes at least one bug where a p2p client would stop trying to
connect after receiving a stale RSN deauth which was reported to
cfg80211 as GO leaving BSS.

Signed-off-by: Thomas Pedersen <c_tpeder@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>